1. Field of the Invention
The invention relates to a camera with an automatic focus adjusting apparatus having a function of locking (referred to as AE lock hereinafter) metered light data according to which an automatic exposure control is carried out upon completion of an automatic focus adjusting operation (which is referred to as AF operation hereinafter).
2. Description of the Prior Art
A camera having an automatic focus adjusting apparatus known in the art and having the above-described function, has been disclosed in the Japanese Laid-open Utility Model Publication No. 148638/1978.
The AE lock operation according to the above-described apparatus is as follows:
(1) An AF operation is started by actuating an AF operation starting button.
(2) When an objective lens is moved to an in-focus position, the in-focus detection is carried out. After the in-focus detection is carried out, AF operations are prohibited and a metered light data is automatically AE locked by operating an AE lock switch provided in addition to a switch for storing metered light data; that is, an AE lock is carried out according to the in-focus detection.
(3) Thereafter, a shutter release button is operated at any desired point to start an exposure control operation; that is, a mirror is turned up by depressing the shutter release button to release a shutter and an exposure control is carried out in accordance with the metered light data which have been locked by the in-focus detection carried out in (2).
Besides the above-described apparatus, a camera provided with an automatic focus adjusting apparatus has been disclosed in the Japanese Laid-open Patent Publication No. 88416/1982 is known in the art. The apparatus is provided with an AE lock button in addition to a focus lock button. The AE lock is carried out either by operating only the AE lock button or only the focus lock button.
The apparatus disclosed in the Japanese Laid-open Utility Model Publication No. 148638/1978, however, has the following disadvantages.
An AE lock cannot be carried out before starting an AF operation which necessitates an operation of an AF operation starting button.
Furthermore, an AE lock cannot be carried out arbitrarily before carrying out in-focus detection. In other words, the apparatus is not provided with an AE lock operation means which can be independently operated, so that an in-focus detection caused AF operation stop cannot be released by an AE lock operation.
Still further, an AE lock according to an in-focus detection is restricted by an AF operation, so that an AE lock operation cannot be carried out at any desired time after an in-focus detection is accomplished.
From the foregoing, the degree of freedom in photography according to this prior art apparatus is low.
The apparatus disclosed in the Japanese Laid-open Patent Publication No. 88416/1982 has the following disadvantages.
(1) An AE lock is performed either by an operation of an AE lock button or a focus lock button and not by a detection of the in-focus condition; that is, an AE lock cannot be automatically carried out according to an in-focus detection. Therefore, an AE lock necessitates an operation of an AE lock button or a focus lock button. Hence, non-preferable operation is necessary.
(2) Since an AE lock is performed by operating a focus lock button, the AE lock cannot be released by an operation of the AE lock button at any desired time; that is, the AE lock state created by the operation of the focus lock button is maintained, so that metered light data cannot be updated. Thus, this prior art apparatus has also a low degree of freedom in photography.
The above-described prior art apparatus disclosed in the Japanese Laid-open Utility Model Publication No. 148638/1978 has two modes in the automatic focus adjusting operation (referred to as AF operation hereinafter) and one mode in manual focus adjusting operation (referred to as FA hereinafter).
In the first mode, light data metered under spot light metering mode is stored when in-focus detection is completed i.e. at the time an AF operation has been completed.
In the second mode, measured light data is stored in unison with a shutter release operation after an AF operation is completed.
In the third mode, metered light data is stored in unison with a shutter release operation after a focus adjustment is manually operated.
The operation of the first mode is as follows:
(1) The first mode is selected by operating a mode selection operation button.
(2) An AF operation is started by operating an AF operation starting button.
(3) When an objective lens is moved to an in-focus position, an in-focus detection is carried out. According to an in-focus detection signal, sequential AF operations are prohibited and metered light data is stored by actuating a memory switch; that is, a AE lock is carried out according to a detection of an in-focus condition.
(4) Thereafter, a shutter release button is operated at any desired moment to start an exposure control operation; that is, a depression of the shutter release button permits a turn-up of a mirror and a start of a shutter release operation, whereby an exposure control operation is carried out according to the metered light data stored by the in-focus detection in (3).
In a photographing operation, according to the first mode, a light metering mode is restricted to spot light metering mode and a portion of an object to which a distance is metered coincides with a portion of the object brightness of which is metered; that is, an object can be photographed in an in-focus and suitable exposure condition even if a target to be photographed is changed after distance metering and an AE lock are carried out.
The prior art apparatus described above, however, has the following disadvantages.
When an object is photographed in the first mode (spot light metering mode) in which an AE lock is carried out according to an in-focus detection, an in-focus detection is impossible when the contrast of an object is low, so that an AE lock cannot be accomplished according to an in-focus detection.
If an exposure control operation is carried out by operating a shutter release button in a condition in which an in-focus detection is impossible, the following disadvantages arise.
There is no quarantee whether or not a main object to be focused is within a focus detecting zone. Moreover, an AE lock operated of metered light data under the spot light metering mode is not carried out upon completion of an AF operation, so that an exposure control is carried out according to the light metering data, under the spot light metering mode, which is obtained when a shutter release button is operated. As a result, an appropriate exposure is not guaranteed.
As apparent from the foregoing, it can be concluded that, considering the case spot light metering data are AE locked according to an AF operation completion (in-focus detection), an inappropriate exposure of an object occurs in the prior art apparatuses when an in-focus detection cannot be carried out because of low contrast of the object.